The combination of high temperatures and relative humidity can induce heat stress in birds.

Limited studies have been performed on the impact of humidity on laying hens because most studies have focused on thermal environments and adjustments.

Researchers investigated the role of relative humidity on production by using 180 Hy-Line brown laying hens (68-wk-old) and dividing them into three treatment groups; Low (25%), Moderate (50%), and High (75%) Relative Humidity (RH). Hens in treatment chambers were kept at 86 degrees F and exposed to the different levels of RH. Parameters were measured in birds and eggs at days 3, 7, 14, 21 and 28 days of trial. Plasma, yolk, and albumen corticosterone (CORT) concentrations were measured. CORT is a key stress hormone in laying hens and measuring CORT in egg yolks is a non-invasive method for assessing a hen’s stress response.

The RH treatments did not affect hen-day egg production, egg weight, feed conversion ratio, or egg mass. Feed intake was lower in the high RH group. The blood H/L ratio (stress indicator) was not affected by RH treatments throughout the experiment, but plasma, egg yolk and albumen CORT concentration was elevated in the High RH group. Relative humidity also changed lipid metabolism and further work is needed to understand if it affects mineral metabolism.

Producer Take Away: Relative humidity at or above 75% in environments at or above 86 degrees F may be an important environmental factor in triggering stress response in laying hens. Birds in these conditions exhibited significantly reduced feed intake, increased stress responses and decreased laying performance and egg quality.